The Humboldt Extension for Ecological Inventories is a new metadata vocabulary that extends the Darwin Core Standard to make it possible to describe the inventories and sampling events that are used to collect organism occurrence data. This is the largest extension to Darwin Core since the original vocabulary was ratified in 2009 and it represents over three years of work by the Humboldt Extension Task Group. This group of international experts met weekly over that time period to develop the vocabulary, carry out implementation testing, and publish the vocabulary and associated documentation.